According to the prior art such as that shown in the U.S. Pat. No. 3,546,377 issued to John Troll on June 12, 1968, an apparatus having two vidicons with delayed scanning means may be used to scan a sample and a standard profile, respectively. As disclosed, the two vidicon outputs are synchronized in time and compared through a differential comparator. A comparator signal output which is above a predetermined threshold is employed to indicate the lack of coincidence and rejection of the sample.